Ultrasound catheter for providing a therapeutic effect to a vessel of a body

ABSTRACT

The invention relates to a catheter system. The system comprises a catheter body having a chamber containing a low acoustic impedance medium. The catheter body includes an elongated body with an external surface and an ultrasound transducer having an external side between a first end and a second end. The ultrasound transducer is positioned over the external surface of the elongated body such that the first end is adjacent to the chamber.

RELATIONSHIP TO CO-PENDING APPLICATIONS

[0001] This application is a continuation-in-part of U.S. patentapplication No. 09/129,980, filed Aug. 5, 1998 and entitled UltrasoundAssembly for Use With a Catheter which is incorporated herein in itsentirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a catheter, and moreparticularly, to a catheter having an ultrasound assembly.

[0004] 2. Description of Related Art

[0005] Many medical treatments can be performed using catheters with anultrasound transducer. These ultrasound transducers deliver ultrasoundenergy to a target site within a patient. The ultrasound energy canprovide a therapeutic effect by itself or can enhance the effects ofother therapeutic media exposed to the ultrasound energy. Inefficientultrasound transducer arrangements can generate excessive heat during amedical treatment.

SUMMARY OF THE INVENTION

[0006] The invention relates to a catheter system. The system comprisesa catheter body having a chamber containing a low acoustic impedancemedium. The catheter body includes an elongated body with an externalsurface and an ultrasound transducer having an external side between afirst end and a second end. The ultrasound transducer is positioned overthe external surface of the elongated body such that the first end ofthe ultrasound transducer is adjacent to the chamber.

[0007] Another embodiment of the system comprises a catheter body havingan external surface. The catheter body includes an ultrasound transducerhaving a side between a first end and a second end. A first medium ispositioned adjacent to the first end of the ultrasound transducer and asecond medium is positioned adjacent to the external side of theultrasound transducer. The second medium is harder than the first mediumto encourage flexibility of the catheter body adjacent to the first endof the ultrasound transducer and efficient transmission of ultrasoundenergy from the external side of the ultrasound transducer.

[0008] The catheter system can also include a sheath for receiving thecatheter.

[0009] The invention also relates to a method for forming a catheter.The method includes positioning an ultrasound transducer over anexternal surface of an elongated body and positioning a collar over theexternal surface of the elongated body such that at least a portion ofthe collar is spaced apart from the ultrasound transducer. The methodalso includes positioning a transducer sheath over at least a portion ofthe ultrasound transducer and over at least a portion of the collar toform a chamber between the ultrasound transducer and the collar.

[0010] Another embodiment of the method includes positioning a firstspacer over an external surface of an elongated body and positioning amember over at least a portion of the first spacer so as to form achamber between the member and the external surface of the elongatedbody. The method also includes positioning an ultrasound transducer overthe member.

[0011] Yet another embodiment of the method includes providing anultrasound transducer having a side between a first end and a secondend. The ultrasound transducer is positioned over an external surface ofan elongated body. The method includes forming a first medium adjacentto the first end of the ultrasound transducer and forming a secondmedium adjacent to the side of the ultrasound transducer. The secondmedium is harder than the first medium to encourage flexibility of thecatheter body adjacent to the first end of the ultrasound transducer andefficient transmission of ultrasound energy from the external side ofthe ultrasound transducer.

BRIEF DESCRIPTION OF THE FIGURES

[0012] FIGS. 1A-1H illustrate a plurality of ultrasound assembles foruse with catheters according to the present invention.

[0013]FIG. 1A is a cross section of an ultrasound assembly having achamber between an ultrasound transducer and an external surface of anelongated body.

[0014]FIG. 1B illustrates the relationship between spacers and theelongated body for the embodiment of the ultrasound assembly illustratedin FIG. 1A.

[0015]FIG. 1C illustrates the relationship between the ultrasoundtransducer and the elongated body for the embodiment of the ultrasoundassembly illustrated in FIG. 1A.

[0016]FIG. 1D illustrates an ultrasound assembly having a chamberadjacent to an end of the ultrasound transducer and a chamber betweenthe ultrasound transducer and the external surface of the elongatedbody.

[0017]FIG. 1E illustrates an ultrasound assembly having chambersadjacent to both ends of the ultrasound transducer and a chamber betweenthe ultrasound transducer and the external surface of the elongated body

[0018]FIG. 1F illustrates an ultrasound assembly having a chamberadjacent to an end of the ultrasound transducer.

[0019]FIG. 1G illustrates an ultrasound assembly having chambersadjacent to both ends of the ultrasound transducer.

[0020]FIG. 1H illustrates an ultrasound assembly without chambers.

[0021] FIGS. 2A-2D illustrate embodiments of ultrasound assemblies foruse with a catheter according to the present invention. The ultrasoundassemblies include a transducer sheath defining a reservoir at the endof the ultrasound assembly. The reservoir contains a binding medium.

[0022] FIGS. 3A-3D illustrate embodiments of ultrasound assemblies foruse with a catheter according to the present invention. The ultrasoundassemblies include an assembly sheath positioned over an ultrasoundtransducer. A volume between the ultrasound transducer and the assemblysheath contains a binding medium.

[0023] FIGS. 4A-4F illustrate ultrasound assemblies having a spacer forcreating a chamber between a side of an ultrasound transducer and anexternal surface of an elongated body. The ultrasound assemblies alsoinclude a collar for creating a chamber adjacent to the ends of theultrasound transducer.

[0024]FIG. 4A illustrates the collar abutting the spacer.

[0025]FIG. 4B illustrates the collar in a spaced apart relationship tothe spacer.

[0026]FIGS. 4C and 4D illustrate the collar positioned over the spacer.

[0027]FIGS. 4E and 4F illustrate the collar integral with the spacer.

[0028]FIG. 5A illustrates a catheter incorporating an ultrasoundassembly.

[0029]FIG. 5B illustrates catheter having a binding medium adjacent tothe ends of the ultrasound transducer.

[0030]FIG. 5C illustrates a catheter having a binding medium adjacent tothe external side of the ultrasound transducer.

[0031]FIG. 5D illustrates a catheter having a binding medium adjacent tothe ends of the ultrasound transducer and another binding mediumadjacent to the external side of the ultrasound transducer.

[0032]FIG. 5E illustrates a catheter having a binding medium adjacent tothe ends of the ultrasound transducer and a second binding mediumadjacent to the external surface of the catheter ultrasound transducerand a third binding medium adjacent to the ultrasound transducer.

[0033]FIG. 5F illustrates a catheter having a binding medium adjacent tothe ends of the ultrasound transducer, a second binding medium adjacentto the external side of the ultrasound transducer and a third bindingmedium positioned in reservoirs at the ends of the ultrasound assembly.

[0034] FIGS. 6A-6C illustrate embodiments of a catheter having aplurality of ultrasound assemblies according to the present invention.

[0035]FIG. 6A illustrates a catheter having ultrasound assemblies spacedapart from a catheter sheath.

[0036]FIG. 6B illustrates a catheter having ultrasound assemblies incontact with a catheter sheath.

[0037]FIG. 6C illustrates a catheter having ultrasound assemblies whichshare a member.

[0038] FIGS. 7A-7E illustrate a method for forming ultrasound assembliesaccording to the present invention.

[0039] FIGS. 8A-8D illustrate a method for forming an ultrasoundassembly when a collar for forming a chamber adjacent to the ultrasoundtransducer is integral with a spacer for forming a chamber between theultrasound transducer and an external surface of an elongated body.

[0040]FIG. 9A illustrates a method for forming an ultrasound assemblyhaving a transducer sheath extending beyond the ultrasound transducerand beyond a collar so as to form reservoirs adjacent to the ends of theultrasound transducer.

[0041]FIG. 9B illustrates delivery of a binding medium into a reservoirat an end of the ultrasound assembly.

[0042] FIGS. 10A-10D illustrate a method for forming a catheteraccording to the present invention.

[0043]FIG. 10A illustrates a catheter sheath positioned over anextension region, an assembly region and a terminal region of a catheterbody.

[0044]FIG. 10B illustrates a binding medium delivered adjacent to an endof the ultrasound transducer.

[0045]FIG. 10C illustrates a binding medium delivered adjacent to anexternal side of the ultrasound transducer.

[0046]FIG. 10D illustrates a first binding medium delivered adjacent toan external side of the ultrasound transducer and a second bindingmedium delivered adjacent to an end of the ultrasound transducer.

[0047]FIG. 11 illustrates the proximal portion of a catheter accordingto the present invention.

[0048] FIGS. 12A-12D illustrate a sheath for use with a catheteraccording to the present invention.

[0049]FIG. 12A is a sideview of the sheath.

[0050]FIG. 12B illustrates a catheter according to the present inventionpositioned within the sheath.

[0051]FIG. 12C is a sideview of a sheath having a drug delivery lumenwhich spirals around a sheath distal end.

[0052]FIG. 12D is a cross section of a sheath having a drug deliverylumen which spirals around a sheath distal end.

[0053] FIGS. 13A-13G illustrate a method for using a catheter accordingto the present invention in conjunction with a sheath.

DETAILED DESCRIPTION

[0054] The invention relates to a catheter having a chamber containing alow acoustic impedance medium. The catheter can also include anelongated body with an external surface. An ultrasound transducer havingan external side between a first end and a second end can be positionedover the external surface of the elongated body such that the first sideof the ultrasound transducer is adjacent to the chamber.

[0055] The low acoustic impedance material within the chamber reducesthe portion of ultrasound energy which is transmitted through thechamber. This reduction causes an increased portion of ultrasound energyto be delivered from the second end of the ultrasound transducer and/orfrom the external side of the ultrasound transducer. As a result, theultrasound energy produced from these sections of the ultrasoundtransducer is delivered with a greater efficiency.

[0056] The ultrasound transducer can be positioned distally relative tothe chamber in order to increase the efficiency of the ultrasound energytransmitted in the distal direction. Alternatively, the ultrasoundtransducer can be positioned proximally relative to the chamber in orderto increase the efficiency of the ultrasound energy transmitted in theproximal direction.

[0057] Another embodiment of the catheter includes a chamber between theelongated body and an internal side of the ultrasound transducer. Thechamber can include a low acoustic impedance medium to reduce theportion of ultrasound energy transmitted into the elongated body. As aresult, the ultrasound energy produced from the ends and the externalside of the ultrasound transducer is delivered with a greater efficiencythan could be achieved without the chamber.

[0058] A catheter according to the present invention can include variouscombinations of the above chambers. Each of the chambers can beindependent of one another or they can be in communication with oneanother. The chambers can contain a low acoustic impedance medium. Forinstance, a catheter can include a first chamber adjacent to the firstend of the ultrasound transducer, a second chamber adjacent to thesecond end of the ultrasound transducer and a third chamber between theinternal side of the ultrasound transducer and the elongated body. As aresult, the ultrasound energy produced from the external surface of thecatheter is delivered at an increased efficiency. Such a catheterefficiently delivers ultrasound energy from the side of the catheter.

[0059] As another example, a catheter can include the first chamberadjacent to the first end of the ultrasound transducer and the thirdchamber between the internal side of the ultrasound transducer and theelongated body. Further, the ultrasound transducer can be positioneddistally relative to the first chamber. The chambers can contain a lowacoustic impedance medium. As a result, the ultrasound energy producedfrom the second end and the external surface of the catheter isdelivered at an increased efficiency. Such a catheter efficientlydelivers ultrasound energy both distally and from the side of thecatheter.

[0060] A catheter according to the present invention can also include aplurality of ultrasound transducers. Each ultrasound transducer can beassociated with one or more chambers. As a result, each ultrasoundtransducer can have an increased efficiency.

[0061] An embodiment of a catheter having a plurality of ultrasoundtransducers includes ultrasound transducers with matched resonantfrequencies. For instance, the catheter can include ultrasoundtransducers selected such that any one has a resonant frequency withinabout 1% of the resonant frequency of any other ultrasound transducer inthe plurality of ultrasound transducers. The matching of the ultrasoundtransducers allows the ultrasound transducers to be concurrently drivenat a single frequency while reducing the inefficiencies associated withdriving ultrasound transducers at a frequency which is significantlydifferent than their resonant frequency.

[0062] Another embodiment of the catheter includes a first bindingmedium adjacent to the first end of the ultrasound transducer and asecond binding medium adjacent to the external side of the ultrasoundtransducer. The first and second media are selected to provide thecatheter with flexibility and a high level of ultrasound transmissionefficiency. Since a softer media is typically more flexible and hardermedia typically transit ultrasound energy more efficiently, the secondmedium is preferably harder than the first medium. The advantages of thefirst and second media are emphasized in multiple ultrasound transducercatheters which tend to lose flexibility with the increased number ofultrasound transducers.

[0063] Catheters according to the present invention can also include anautotransformer in the proximal portion of the catheter. Theautotransformer can serve to adjust the characteristic impedance of thecatheter to match the impedance of components used to drive the one ormore ultrasound transducers included on the catheter. The matchedimpedance serves to increase the efficiency of the catheter system.

[0064] Catheters according to the present invention can also include acatheter identification electronics. The catheter identificationelectronics indicate to a catheter control system the frequency thatultrasound transducers should be driven.

[0065] FIGS. 1A-1C illustrate an embodiment of an ultrasound assembly 10according to the present invention for use with a catheter according tothe present invention. FIG. 1A is a longitudinal cross sectional view ofthe ultrasound assembly 10. FIG. 1B is a lateral cross section of theultrasound assembly 10 taken at the point labeled A in FIG. 1A. FIG. 1Cis a lateral cross section of the ultrasound assembly 10 taken at thepoint labeled B in FIG. 1A.

[0066] The ultrasound assembly 10 includes an elongated body 12 with anexternal surface 14. A plurality of spacers 16 are positioned over theexternal surface 14 of an elongated body 12 and a member 18 ispositioned over at least a portion of the spacers 16. The ultrasoundassembly 10 also includes an ultrasound transducer 20 with an externalside 22 and an internal side 24 between a first end 26 and a second end28. The ultrasound transducer 20 is positioned over the member 18 andcan surround the member 18. Suitable materials for the member 18include, but are not limited to, polyimide, polyester and nylon. Asuitable ultrasound transducer 20 includes, but is not limited to,PZT-4D, PZT-4, PZT-8 and various piezoceramics.

[0067] The internal side 24 of the ultrasound transducer 20, the spacers16 and the member 18 each define a portion of a chamber 30 between theinternal side 24 of the ultrasound transducer 20 and the externalsurface 14 of the elongated body 12. The chamber 30 preferably has aheight from 0.25-10 μm, more preferably from 0.50-5 μm and mostpreferably from 0.0-1.5 μm.

[0068] The member 18 can extend beyond the first end 26 and/or thesecond end 28 of the ultrasound transducer 20. Additionally, the spacers16 can be positioned beyond the ends of the ultrasound transducer 20. Asa result, the chamber 30 can extend along the longitudinal length of theultrasound transducer 20 to increase the portion of the ultrasoundtransducer 20 which is adjacent to the chamber 30.

[0069] The chamber 30 can contain a low acoustic impedance medium.Suitable low acoustic impedance media include, but are not limited to,fluids such as helium, argon, air and nitrogen and/or solids such assilicone and rubber. The chamber 30 can also be evacuated. Suitablepressures for an evacuated chamber 30 include, but are not limited to,negative pressures to −760 mm Hg.

[0070] As illustrated in FIG. 1D, the internal side 24 of the ultrasoundtransducer 20 can also be positioned adjacent to a chamber 30. Theultrasound assembly 10 includes a collar 32 over external surface 14 ofthe elongated body 12. The collar 32 can surround the elongated body 12.The collar 32 has a spaced apart relationship to the ultrasoundtransducer 20.

[0071] A transducer sheath 34 is positioned over at least a portion ofthe ultrasound transducer 20 and the collar 32 to form a chamber 30adjacent to a side of the ultrasound transducer 20. An inner side of thecollar 32, the ultrasound transducer 20 and the transducer sheath 34each partially define the chamber 30. The chamber 30 preferably has awidth, W, from 12-2500 μm, more preferably from 25-250 μm and mostpreferably from 25-125 μm. The chamber 30 can contain a low acousticimpedance medium. Suitable materials for the transducer sheath 34include, but are not limited to air, N², O², and vacuum. The transducersheath 34 preferably has a thickness from 10-100 μm and more preferablyfrom 25-50 μm.

[0072] The ultrasound assembly 10 can also include a chamber 30 adjacentto the second end 28 of the ultrasound transducer 20 as illustrated inFIG. 1E. A second collar 36 is positioned over the elongated body 12 andcan surround the external surface 14 of the elongated body 12. Thesecond collar 36 has a spaced apart relationship from the ultrasoundtransducer 20 so as to provide a second chamber 30 adjacent to theultrasound transducer 20. An inner side of the second collar 36, theultrasound transducer 20 and the transducer sheath 34 each partiallydefine the chamber 30. The chamber 30 preferably has a width, W, from12-2500 μm, more preferably from 25-250 μm and most preferably from25-125 μm. The chamber 30 adjacent to the second end 28 of theultrasound transducer 20 can also contain a low acoustic impedancemedium.

[0073] Each of the chambers can be isolated from one another. However,when the ultrasound assembly 10 includes a chamber 30 between theultrasound transducer 20 and the elongated body 12, one or more of thespacers 16 can be formed of a porous material to provide communicationbetween the chambers 30. This communication can permit the pressures ineach of the chambers 30 to reach an equilibrium. Alternatively, one ormore of the spacers 16 can include channels, lumens 38 and/or a ridgedexternal surface to permit the communication between chambers 30.

[0074] An embodiment of the ultrasound assembly 10 does not include achamber 30 between the elongated body 12 and the internal side 24 of theultrasound transducer 20 as illustrated in FIG. 1F. The ultrasoundtransducer 20 is positioned adjacent to the external surface 14 of theelongated body 12 such that a chamber 30 is not formed between theelongated body 12 and the ultrasound transducer 20. The ultrasoundassembly 10 includes a collar 32 around the elongated body 12 in aspaced apart relationship from the ultrasound transducer 20 so as toform a chamber 30 adjacent to the first side of the ultrasoundtransducer 20.

[0075] The ultrasound assembly 10 of FIG. 1F can also include a secondchamber 30 adjacent to the second end 28 of the ultrasound transducer 20as illustrated in FIG. 1G. The ultrasound assembly 10 includes a secondcollar 36 over the elongated body 12 in a spaced apart relationship fromthe ultrasound transducer 20. Accordingly a second chamber 30 is formedadjacent to the second side of the ultrasound transducer 20. Asillustrated in FIG. 1H, an embodiment of the ultrasound assembly 10 doesnot include any chambers 30.

[0076] A utility lumen 38 extends through the elongated body 12. Theutility lumen 38 can be sized to receive a guidewire, to delivertherapeutic media including drugs, medication, microbubbles and othercompounds which provide a therapeutic effect. Although, the elongatedbody 12 is illustrated as having a single utility lumen 38, theelongated body 12 can include a plurality of lumens 38 or can be solid.

[0077] Each of the ultrasound assemblies 10 illustrated in FIGS. 1A-1Hcan have a transducer sheath 34 which extends past the first collar 32,the second collar 36 and/or past the ultrasound transducer 20. FIGS.2A-2D illustrate such a transducer sheath 34 with a selection of theultrasound assemblies 10 illustrated in FIGS. 1A-1H. The extension ofthe transducer sheath 34 past the collar 32 and/or past the ultrasoundtransducer 20 provides a reservoir 40 at the ends of the ultrasoundassembly 10. The reservoir 40 can optionally contain a binding medium 42such as an epoxy or adhesive. The binding medium 42 can serve to keepthe ultrasound transducer 20 intact during the handling of theultrasound assembly 10. Although FIGS. 2A-2D illustrate the transducersheath 34 extending past the first collar 32, the second collar 36and/or the ultrasound transducer 20 at both ends of the ultrasoundassembly 10, the transducer sheath 34 can extending past a collar 32and/or ultrasound transducer 20 at only one end of the ultrasoundassembly 10.

[0078] Each ultrasound assembly 10 discussed and/or suggested above caninclude an assembly 10 sheath. FIGS. 3A-3D illustrate a selection of theabove ultrasound assemblies 10 including an assembly sheath 44positioned over the ultrasound transducer 20. Suitable materials for theassembly sheath 44 include, but are not limited to polyimide, PTFE, andpolyurethane. The assembly sheath 44 preferably has a thickness from12-75 μm and more preferably from 25-50 μm.

[0079] A volume between the assembly sheath 44 and the ultrasoundtransducer 20 can contain a binding medium 42 as illustrated in FIG. 3A.Further, when the ultrasound assembly 10 includes a transducer sheath34, the volume between the ultrasound assembly 10 sheath and thetransducer sheath 34 can contain the binding medium 42 as illustrated inFIGS. 3B-3D. The binding medium 42 can be a binding medium 42 whichserves to keep the ultrasound transducer 20 intact during the handlingof the ultrasound assembly 10.

[0080] Each of the ultrasound assemblies 10 illustrated above show theelongated body 12 extending outward from the ultrasound assembly 10.However, the elongated body 12 can be trimmed to provide an elongatedbody 12 which is flush with one or more sides of the elongated body 12.Additionally, a sensor such as a temperature sensor can be positioned inthe binding medium 42 associated with any of the above ultrasoundassemblies 10.

[0081] FIGS. 4A-4F illustrate various arrangements between the collars32 and spacers 16 for use with the ultrasound assemblies 10 discussedabove. FIG. 4A illustrates the collar 32 abutting the spacers 16. Thecollar 32 can be spaced apart from the spacers 16 as illustrated in FIG.4B. In another embodiment, the collar 32 is sized to be positionedaround the spacer 16 as illustrated in FIG. 4C. In yet anotherembodiment, the collar 32 is sized to be positioned around the member 18as illustrated in FIG. 4D.

[0082] The collar 32 can be integral with the spacers 16 as illustratedin FIG. 4E. The spacer 16 has an L-shaped profile with a spacer region46 positioned adjacent to the member 18 and a collar region 48positioned adjacent to the transducer sheath 34. Accordingly, the raisededge serves to define a side of the chamber 30. When the collar 32 isintegral with the spacer, the spacer 16 can include a seat 50 sized toreceive an edge of the member 18 as illustrated in FIG. 4F.

[0083]FIGS. 5A and 5B illustrate a catheter according to the presentinvention. The catheter can include any of the ultrasound assemblies 10discussed or suggested above. As a result, the catheter is illustratedwith a generalized representation of an ultrasound assembly 10.Specifically, an ultrasound assembly 10 is illustrated as an ultrasoundtransducer 20 over an elongated body 12. A box 51 over the ultrasoundtransducer 20 represents the remaining portions of each ultrasoundassembly 10. For instance, the box 51 can represent the collars 32,spacers, members, chambers, binding media, etc. associated with anultrasound assembly 10.

[0084] The catheter includes a catheter body 52 having an externalsurface 53, a distal portion 54 and a proximal portion 56. The catheterbody 52 can include an extension region 58, an assembly region 60 and aterminal region 62. Lumens 38 within the extension region 58, assemblyregion 60 and terminal region 62 are aligned with one another to provideone or more lumens 38 extending through the entire catheter. Theselumens 38 can be sized to receive a guidewire or for the delivery of atherapeutic agent such as a drug.

[0085] The extension region 58 includes an extension body 64 having oneor more lumens 38. The one or more lumens 38 included in the extensionbody 64 have cross sectional dimensions approximating the cross sectiondimensions of the one or more utility lumens 38 of the elongated body12. The extension body 64 can be used to add length to the catheter.Specifically, the extension body 64 can provide additional length beyondthe length provided by the assembly region 60. Accordingly, theextension body 64 can be short or can be eliminated from the catheterbody 52. Suitable materials for the extension body 64 include, but arenot limited to, polyimide, silicone, and polyurethane.

[0086] The terminal region 62 is positioned at the distal tip of thecatheter. The terminal region 62 includes a terminal body 66. Theterminal body 66 can be solid or include one or more lumens 38 withcross sectional dimensions approximating the cross section dimensions ofthe one or more utility lumens 38 of the elongated body 12. Suitablematerials for the terminal region 62 include, but are not limited to,polyimide, silicone, and polyurethane. The assembly region 60 is theregion of the catheter body 52 including any of the ultrasoundassemblies 10 discussed and/or suggested above.

[0087] A catheter sheath 68 is positioned over the extension region 58,the assembly region 60 and the terminal region 62 so as to define aportion of the external surface 53 of the catheter body 52. The cathetersheath 68 can serve to immobilize the extension region 58, the assemblyregion 60 and the terminal region 62 relative to one another. Thecatheter sheath 68 is optional and can be removed from the catheter body52.

[0088] The volume between the ultrasound assembly 10 and the extensionbody 64 can contain a binding medium 42. Such binding media can serve tocouple the extension region 58, the assembly region 60 and the terminalregion 62 together. Suitable materials for the catheter sheath 68include, but are not limited to polyethelyne, polyurethane, andpolyimide. The thickness of the catheter sheath 68 material ispreferably 0.001″ to 0.020″, more preferably 0.004″ to 0.010″ and mostpreferably 0.006″ to 0.008″.

[0089] As illustrated in FIG. 5B, a first binding medium 42A can bepositioned adjacent to the ends of the ultrasound transducer 20.Specifically, a volume between the extension body 64 and the ultrasoundtransducer 20 can contain the first binding medium 42A. Further, thevolume between the terminal body 66 and the ultrasound transducer 20 cancontain the first binding medium 42A.

[0090] The first binding medium 42A can also be positioned adjacent tothe external side 22 of the ultrasound transducer 20 as illustrated inFIG. 5C. Specifically, the first binding medium 42A can be contained ina volume between the external side 22 of the ultrasound transducer 20and the externals surface of the catheter body 52.

[0091] As illustrated in FIG. 5D, a catheter can include a first bindingmedium 42A and a second binding medium 42B. The first binding medium 42Ais adjacent to the ends of the ultrasound transducer 20 and the secondbinding medium 42B is adjacent to the external side 22 of the ultrasoundtransducer 20. Specifically, the second binding medium 42B can becontained in a volume between the external side 22 of the ultrasoundtransducer 20 and the external surface 53 of the catheter body 52. Aportion of the second binding medium 42B is also illustrated as beingadjacent to the ends of the ultrasound assembly 10 although the secondbinding medium 42B can be restricted to the volume adjacent to theexternal side 22 of the ultrasound transducer 20.

[0092] The first binding medium 42A and the second binding medium 42Bcan be the same or different. When the second binding medium 42B isdifferent than the first binding medium 42A, the second binding medium42B is preferably harder than the first binding medium 42A. A harderbinding medium 42 typically transmits ultrasound energy more efficientlythan a softer binding medium 42. As a result, the hardness of the secondbinding medium 42B can preserve the ultrasound transmitting efficiencyof the catheter. Additionally, the softness of the first binding medium42A provides the catheter with additional flexibility. As a result, thechoices of the first and second binding media effect both theflexibility and the ultrasound transmission efficiency of the catheter.

[0093] The second binding medium 42B is preferably at least 2 timesharder than the first binding medium 42A and more preferably from about3 to about 5 times harder than the first binding medium 42A. The firstbinding medium 42A preferably has a hardness of at least about 10 ShoreD, more preferably from about 15 to about 80 Shore D and most preferablyfrom about 20 to about 40 Shore D. The second binding medium 42Bpreferably has a hardness of at least about 60 Shore D, more preferablyfrom about 65 to about 120 Shore D and most preferably from about 80 toabout 100 Shore D.

[0094] As described above, any of the ultrasound assemblies 10 describedand/or suggested above can be included in a catheter according to thepresent invention. FIG. 5E illustrates a particular example of acatheter including an assembly sheath 44 over the ultrasound transducer20. Specifically, FIG. 5B illustrates the catheter including theultrasound assembly 10 of FIG. 2B. The ultrasound assembly 10 includes achamber 30 adjacent to a first end 26 of the ultrasound transducer 20.The chamber 30 is positioned proximally relative to the ultrasoundtransducer 20. The ultrasound assembly 10 includes another chamber 30between the ultrasound transducer 20 and the external surface 14 of theelongated body 12. Each chamber 30 contains a low acoustic impedancemedium. As a result, this embodiment of the catheter efficientlytransmits ultrasound energy in the distal direction.

[0095] The catheter of FIG. 5E includes a first binding medium 42A, asecond binding medium 42B and a third binding medium 42C. The firstbinding medium 42A is adjacent to the ends of the ultrasound transducer20 and the second binding medium 42B is contained in a volume betweenthe assembly sheath 44 and the external surface 53 of the catheter body52. The third binding medium 42C is adjacent to the external side 22 ofthe ultrasound transducer 20. Specifically, a volume between theultrasound transducer 20 and the assembly sheath 44 includes the thirdbinding medium 42C.

[0096] Two or more of the first, second and third binding media can bethe same or they can all be different. In a preferred embodiment, thefirst and second binding media are the same while the third bindingmedium 42C transmits is harder than the first and second binding media.Accordingly, when the first and second binding media are the same, thethird binding media is preferably harder than the first binding medium42A. Preferably, the first binding medium 42A is also more flexible thanthe third binding medium 42C. Further, the third binding medium 42C ispreferably at least 2 times harder than the first binding medium 42A andmore preferably from about 3 to about 5 times harder than the firstbinding medium 42A. Additionally, the first binding medium 42Cpreferably has a hardness of at least about 10 Shore D, more preferablyfrom about 15 to about 80 Shore D and most preferably from about 20 toabout 40 Shore D. The third binding medium 42B preferably has a hardnessof at least about 60 Shore D, more preferably from about 65 to about 120Shore D and most preferably from about 80 to about 100 Shore D. Inanother preferred embodiment, the second and third binding media areeach harder than the first binding medium 42A. In another preferredembodiment, the second and third binding media are the same and areharder than the first binding medium 42A.

[0097]FIG. 5F illustrates a particular example of a catheter having atransducer sheath 34 extending beyond the collar 32 and the ultrasoundtransducer 20 to form reservoirs 40 at the end of the ultrasoundassembly 10. The catheter includes a first binding medium 42A, a secondbinding medium 42B and a third binding medium 42C. The first bindingmedium 42A is adjacent to the ends of the ultrasound transducer 20 andthe second binding medium 42B is adjacent to the external side 22 of theultrasound transducer 20. Reservoirs 40 formed adjacent to the ends ofthe ultrasound transducer 20 contain the third binding medium 42C.

[0098] Two or more of the first, second and third binding media can bethe same or they can all be different. The second binding medium 42Bpreferably transmits ultrasound energy more efficiently than the firstbinding medium 42A. Further, the first binding medium 42A is preferablymore flexible than the second binding medium 42B. The first and secondbinding media preferably have the hardness relationships and levelsdescribed with respect to the first and second binding media of FIG. 5D.In a preferred embodiment, the first and third binding media are thesame.

[0099] The catheter can include two or more ultrasound assemblies 10 asillustrated in FIGS. 6A and 6B. FIG. 6A illustrates the ultrasoundassembly 10 in contact with the catheter sheath 68 while FIG. 6Billustrates the ultrasound assemblies 10 spaced apart from the cathetersheath 68. The ultrasound assemblies 10 can share the same elongatedbody 12 and/or different ultrasound assemblies 10 can include differentelongated bodies 12. When the ultrasound assemblies 10 are formed withdifferent elongated bodies 12, the different elongated bodies 12 can bealigned with one another during assembly of the catheter.

[0100] Two or more ultrasound assemblies 10 can share a member 18 asillustrated in FIG. 6C. Each of the ultrasound assemblies 10 ispositioned over the same member 18. As a result, the member 18 partiallydefines a chamber 30 between each of the ultrasound transducers 20 andthe elongated body 12. When different ultrasound transducers 20 share amember 18, spacers 16 can be optionally positioned between theultrasound assemblies 10. As a result, a single member 18 can bepositioned over at least a portion of three or more spacers 16.

[0101] As illustrated in FIGS. 6A and 6B, when the catheter includes aplurality of ultrasound transducers 20, a first binding medium 42A canbe positioned adjacent to the ends of the ultrasound transducers 20.Specifically, the first binding medium 42A can be contained in a volumebetween an ultrasound transducer 20 and an extension body 64, a volumebetween adjacent ultrasound transducer 20, and/or a volume between anultrasound transducer 20 and a terminal body 66.

[0102] As illustrated in FIG. 6C, a catheter including a plurality ofultrasound assemblies 10 can also include a second binding medium 42Badjacent to the external side 22 of the ultrasound transducers 20.Specifically, the second binding medium 42B can be contained in a volumebetween the external side 22 of the ultrasound transducer 20 and theexternal surface 53 of the catheter body 52. As described with respectto FIG. 5D, the first and second binding media can be the same ordifferent and the second binding medium 42B is preferably harder thanthe first binding medium 42A. As described with respect to FIGS. 5E-5F,the inclusion of specific ultrasound assembly 10 embodiments can resultin the catheter including additional binding media. When the catheterincludes an additional binding media adjacent to the external side 22 ofthe ultrasound transducers 20 (i.e. FIG. 5E), that binding media ispreferably at least as hard as the first and second binding media.

[0103] FIGS. 7A-7E illustrate a method for fabricating ultrasoundassemblies 10 according to the present invention. In FIG. 7A, spacers 16are positioned over an elongated body 12. The spacers 16 can optionallybe adhesively attached to the elongated body 12 with compounds such asepoxy. FIG. 7B illustrates a member 18 positioned over the spacers 16.The positioning of the member 18 forms a chamber 30 between the member18 and the elongated body 12. The member 18 can optionally be adhesivelyattached to the spacers 16 with compounds such as epoxy.

[0104] In FIG. 7C an ultrasound transducer 20 is positioned over themember 18 to form the ultrasound assembly 10 of FIG. 1A. The ultrasoundtransducer 20 can optionally be adhesively attached to the member 18with compounds such as epoxy. A collar 32 is also positioned over theelongated body 12 and can be attached to the elongated body 12 withcompounds such as epoxy. FIG. 7D illustrates a transducer sheath 34positioned over the collar 32 to form the ultrasound assembly 10 of FIG.2B. The transducer sheath 34 forms a chamber 30 adjacent to theultrasound transducer 20.

[0105] In FIG. 7E an assembly sheath 44 is positioned over thetransducer sheath 34 of the ultrasound assembly 10 illustrated in FIG.7D. A binding medium 42 precursor is delivered adjacent to the externalside 22 of the ultrasound transducer 20. Specifically, the bindingmedium 42 precursor is delivered into a volume between the transducersheath 34 and the assembly sheath 44. The binding medium 42 can bedelivered into the volume using an injection device such as a hypodermicneedle 70. The binding medium 42 can solidify to provide the ultrasoundassembly 10 of FIG. 3B. Suitable mechanisms for solidification include,but are not limited to, setting, cooling and curing.

[0106] FIGS. 8A-8D illustrate method for forming ultrasound assemblies10 when the collar 32 is integral with the spacers 16. FIG. 8Aillustrates a spacer 16 positioned over an elongated body 12. In FIG. 8Ba member 18 is positioned over the spacer 16 and an ultrasoundtransducer 20 is positioned over the member 18. In FIG. 8C a secondspacer 16 is positioned over the elongated body 12 and moved toward theoriginal spacer 16 until a portion of the spacer 16 is positionedbetween the member 18 and the elongated body 12. As a result, a chamber30 is formed between the member 18 and the elongated body 12. In FIG. 8Da transducer sheath 34 is positioned over the spacers 16 and theultrasound transducer 20 to form the ultrasound assembly 10 of FIG. 3Chaving collars 32 which are integral with the spacers 16.

[0107] FIGS. 9A-9B illustrate an adaptation of the method illustrated inFIGS. 7A-7E to form an ultrasound assembly 10 having a transducer sheath34 which extends past a first collar 32, a second collar 36 and/or pastthe ultrasound transducer 20 as discussed with respect to FIGS. 2A-2D.FIG. 9A illustrates a transducer sheath 34 positioned over the collar 32and ultrasound transducer 20 of FIG. 7C. The ultrasound transducer 20extends past the collar 32 and the ultrasound transducer 20 to formreservoirs 40 adjacent to the ends of the ultrasound transducer 20. FIG.9B illustrates a binding medium 42 precursor being delivered into thereservoirs 40 to provide the ultrasound assembly 10 illustrated in FIG.2B.

[0108] The methods described in FIGS. 7A-9B can be used to provide anelongated body 12 having a plurality of ultrasound assemblies 10. Eachultrasound assembly 10 can be concurrently formed on the elongated body12 or they can be sequentially formed on the elongated body 12.Alternatively, a portion of each ultrasound assembly 10 can be formedconcurrently while the remaining portions of the ultrasound assemblies10 are formed sequentially. For instance, in FIG. 6C, the chamber 30between each ultrasound transducer 20 and the external surface 14 of theelongated body 12 can be formed concurrently while the remainingportions of the ultrasound assemblies 10 are formed sequentially.

[0109] FIGS. 10A-10D illustrate methods for forming a catheter accordingto the present invention. FIG. 10A illustrates a catheter sheath 68positioned over an extension body 64 as illustrated by the arrow labeledA. The ultrasound assembly 10 is then positioned within the cathetersheath 68 as illustrated by the arrow labeled B. A terminal body 66 isthen positioned within the catheter sheath 68 as indicated by the arrowlabeled C.

[0110] As illustrated in FIG. 10B, a binding medium 42 precursor isdelivered adjacent to an end of the ultrasound transducer 20.Specifically, the binding medium 42 precursor is delivered into a volumebetween the ultrasound assembly 10 and the terminal body 66. FIG. 10Billustrates the binding medium 42 precursor delivered adjacent to an endof the ultrasound assembly 10 using an injection instrument such as ahypodermic needle 70. The binding medium 42 precursor can besequentially delivered adjacent to one end of the ultrasound transducer20 and then adjacent to the opposing end of the ultrasound transducer20. The binding medium 42 precursor preferably solidifies to form abinding media adjacent to the ends of the ultrasound transducer 20.

[0111] As illustrated in FIG. 10C, a binding medium 42 precursor canalso be delivered into a volume between the external side 22 of theultrasound transducer 20 and the external surface 53 of the catheterbody 52. As illustrated, the quantity of binding medium 42 precursordelivered can be enough to fill the volume adjacent to the external side22 of the ultrasound transducer 20. The binding medium 42 precursorpreferably solidifies to form a binding medium 42 adjacent to theexternal side 22 of the ultrasound transducer 20. Alternatively,sufficient binding medium 42 precursor can be delivered to fill thevolume adjacent to the ends of the ultrasound transducer 20.

[0112] When the quantity of binding medium 42 precursor delivered fillsthe volume adjacent to the external side 22 of the ultrasound transducer20, a second binding medium 42B precursor can be delivered into thevolumes adjacent to the ends of the ultrasound transducer 20 asillustrated in FIG. 10D. The second binding medium 42B precursorpreferably solidifies to form a second binding medium 42B adjacent tothe ends of the ultrasound transducer 20.

[0113] Once the binding media delivered above have solidified, thecatheter sheath 68 can be removed from the catheter body 52.Additionally, once a chamber 30 is formed, a fluid low acousticimpedance medium can be delivered into the chamber 30. A low acousticimpedance medium preferably has an acoustic impedance less than about1.7 Megarayls, more preferably of about 0-0.7 Megarayls and mostpreferably from 0-0.4 Megarayls. As described above, suitable lowacoustic impedance media include, but are not limited to, helium, argon,air and nitrogen. These media can be delivered into the chamber 30during or after the media solidification process using an injectiondevice such as a hypodermic needle 70. Similar techniques can be used todraw a vacuum within the chamber 30. Solid low acoustic impedance mediasuch as silicones and rubbers can be positioned within the chamber 30during the formation of the ultrasound assembly 10.

[0114] The methods for forming a catheter described with respect toFIGS. 10A-10D can be used to form a catheter having multiple ultrasoundassemblies 10. For instance, the elongated body 12 illustrated in FIG.10A can be replaced with an elongated body 12 having a plurality ofultrasound assemblies 10. Alternatively, several independent elongatedbodies 12 having ultrasound assemblies 10 can be sequentially positionedwithin the catheter sheath 68. The one or more lumens 38 in adjacentelongated bodies 12 are aligned before binding medium 42 precursor isdelivered into the volume defined by the catheter sheath 68. Additionalcatheters having a plurality of ultrasound transducers are described inU.S. patent application No. 09/071,285, filed May 1, 1998 and entitledUltrasound Catheter for Providing a Therapeutic Effect to a Vessel of aBody which is incorporated herein in its entirety.

[0115] When the ultrasound assembly 10 or catheter includes multipleultrasound transducers 20, the methods for forming the ultrasoundassembly 10 or catheter can include matching the resonant frequencies ofthe ultrasound transducers 20. For instance, the ultrasound transducers20 can be selected such that any member of the plurality of ultrasoundtransducers 20 has a resonant frequency within about 10% of the resonantfrequency of any other ultrasound transducer 20. More preferably, theultrasound transducers 20 are selected such that any one has a resonantfrequency within about 3%, even more preferably within about 1% and mostpreferably within about 0.5% of any other ultrasound transducer 20 inthe plurality of ultrasound transducers 20. The selected ultrasoundtransducers 20 are then used to form an ultrasound assembly 10 orcatheter.

[0116] The matching of the ultrasound transducers 20 allows theultrasound transducers to be concurrently driven at a single frequencywhile reducing the inefficiencies associated with driving ultrasoundtransducers 20 at a frequency which is significantly different thantheir resonant frequency. Since the ultrasound transducers 20 can bedriven at a single frequency, the matching the resonant frequencies ofthe ultrasound transducers 20 is preferred when the plurality ofultrasound transducers 20 are connected in parallel or in series.

[0117] The electrical connections for driving the one or more ultrasoundtransducers 20 can be done at various stages during the assembly of thecatheter and/or ultrasound assembly 10. For instance, electrical wirescan be coupled with the ultrasound transducers 20 before the ultrasoundtransducers 20 are positioned over the elongated body. Additionally, theelectrical wires can be coupled with the ultrasound transducers 20 afterthe ultrasound transducers 20 are in position over the elongated body.Further, electrical connections can be made alternating with positioningthe ultrasound transducers 20 over the elongated body.

[0118] Alternatively, one or more electrical wires can be positionedalong the elongated body before the ultrasound transducers 20 arepositioned over the elongated body. One or more ultrasound transducers20 can then be slid over the elongated body such that the one or moreelectrical wires contact the inner side of the ultrasound transducers20. The contact between the ultrasound transducers 20 and the electricalwire can serve as the electrical connection to the one or moreultrasound transducers 20. When a catheter or ultrasound assembly 10includes more than one ultrasound transducer 20, the ultrasoundtransducers 20 can be connected in parallel, in series or independentlyconnected. Wires extending from the one or more ultrasound transducers20 can be threaded up through one or more lumens 38 in the extensionbody 64.

[0119] During the formation of the catheter and/or formation of theultrasound assemblies 10, one or more sensors can be included in any ofthe media described above. The sensor can be positioned within a volumebefore a medium is delivered into the volume. Alternatively, the sensorcan be delivered into a binding medium 42 precursor while the bindingmedium 42 precursor is in a flowable state. Wires extending from the oneor more sensors can be threaded up through one or more lumens 38 in theextension body 64. Suitable sensors for use with the catheter include,but are not limited to, a temperature sensor. When a catheter includesone or more temperature sensors, the temperature sensor is preferablypositioned adjacent to the external side 22 of an ultrasound transducer20. Specifically, the one or more temperature sensors are preferablypositioned in a volume between the external side 22 of the ultrasoundtransducer 20 and the external surface 53 of the catheter body 52.

[0120] The solidification of the binding medium 42 precursors can occurconcurrently or independently of one another. As discussed with respectto FIGS. 5A-5F, the binding medium 42 precursor and the second bindingmedium 42B precursor preferably solidify to different degrees ofhardness.

[0121] Binding medium 42 precursors for use with the catheters andultrasound assemblies 10 discussed above are preferably flowable tooptimize delivery into a desired volume. These precursors preferablysolidify to a binding medium 42 having a reduced flowability. Theseprecursors more preferably solidify to a binding medium 42 having areduced flowability and an increased degree of adhesiveness. Thissolidification can occur through mechanisms including, but not limitedto, cooling, setting and curing. Suitable binding media precursorsand/or binding media include, but are not limited to, adhesives,epoxies, polymers, plastics, rubbers. Examples of suitable binding mediawith different degrees of hardness are EPOTEK 310 having a hardness ofabout 22 Shore D and HYSOL 3561 and 2939 having a hardness of about 85Shore D. The binding media to be used can be selected for its particularhardness. Alternatively, binding media, such as epoxies, cure to adifferent hardness based on the component ratio in the binding media.The component ratio can be adjusted to achieve the desired hardness.

[0122] The binding media adjacent to the external side 22 of theultrasound transducer 20 and/or adjacent to the ends of the ultrasoundtransducer 20 preferably has an acoustic impedance of about 1-20Megarayls, more preferably about 1.3-10 Megarayls and most preferablyabout 4-8 Megarayls. As described above, the low acoustic impedancemedium contained within the chambers preferably has an acousticimpedance less than about 1.7 Megarayls, more preferably of about 0-0.7Megarayls and most preferably from 0-0.4 Megarayls. Further, the ratioof the acoustic impedances for the binding medium adjacent to theexternal side and/or adjacent ends the of the ultrasound transducer 20measured relative to the acoustic impedance of the low acousticimpedance medium contained within the chambers is preferably at least1.5:1, more preferably at least 2:1 and most preferably at least 4:1.Additionally the ratio is preferably 1.5:1 to 10,000:1, more preferablyabout 1.5:1 to 100:1 and most preferably 1.5:1 to 4:1.

[0123]FIG. 11 illustrates the proximal portion 72 of a catheteraccording to the present invention. An electrical coupling 74 extendsfrom the proximal portion 72 of the catheter. The electrical coupling 74can be coupled with a catheter control system (not shown) for adjustingthe frequency and power of ultrasound energy delivered from thecatheter. These adjustments can be made in response to signals from oneor more sensors included with the catheter. For instance, theseadjustments can be made in response to signals form a temperature sensorin order to maintain the temperature at a treatment site within aparticular range.

[0124] The electrical coupling 74 includes an autotransformer 76 foradjusting the characteristic impedance of the catheter to match theimpedance of an amplifier included in the catheter control system. Forinstance, if the amplifier has an input impedance of 50 ohms and thecatheter has a characteristic impedance of 40 ohms, the addition of theautotransformer can provide the catheter with a characteristic impedanceof about 50 ohms. The matched impedance serves to increase theefficiency of the catheter system.

[0125] Because each catheter can have a different characteristicimpedance, the windings on the autotransformer can be adjusted to matchthe particular catheter of interest. As a result, a method of assemblinga catheter can include the step of providing an autotransformer whichmatches the characteristic impedance of the catheter to thecharacteristic impedance of a component in a catheter control system.

[0126] The electrical coupling also includes catheter identificationelectronics 78. The catheter identification electronics 78 indicate tothe catheter control system what frequency the catheter should bedriven. For instance, the catheter identification electronics 78 can beone or more resistors. The catheter control system can include logic foridentifying the resistance. This resistance can be associated with acatheter of a particular frequency. The logic can identify theparticular frequency of the catheter and can then cause the catheter tobe driven at the indicated frequency. A computer chip is another exampleof suitable catheter identification electronics 78. The computer chipcan produce signals indicating the frequency of the catheter to thecatheter control system. In response, the catheter control system candrive the catheter at the appropriate frequency.

[0127] A catheter according to the present invention can be used byitself or can be used in conjunction with a sheath 82 as illustrated inFIGS. 12A-12D. Additional sheath and catheter embodiments are providedin U.S. patent application No. 09/107,078, filed Jun. 29, 1998 andentitled Sheath for Use with an Ultrasound Element which is incorporatedherein in its entirety. FIG. 12A illustrates a sheath 82 configured toreceive the catheter. The sheath 82 includes a sheath proximal end 84and a sheath distal end 86. A catheter receiving lumen 88 extendsthrough the sheath 82 and is sized to receive the catheter asillustrated in FIG. 12B. The sheath distal end 86 preferably includes anenergy delivery portion which is constructed from a material whichefficiently transmits ultrasound energy. Suitable materials for both thesheath 82 and the energy delivery section 90 include, but are notlimited to, polyethylene.

[0128] The catheter can be rotated or moved within the sheath 82 asillustrated by the arrow labeled A. The movement of the catheter withinthe sheath 82 can be caused by manipulating the proximal portion of thecatheter body 52 while holding the sheath proximal end 84 stationary.Although not illustrated, the sheath distal end 86 can include on ormore temperature sensors.

[0129] As illustrated in FIGS. 12C-12D, the sheath 82 can alsooptionally include a drug delivery lumen 92. The drug delivery lumen 92can include one or more drug delivery ports 94 through which a drug canbe delivered. The drug delivery lumen 92 can be straight but ispreferably curved and more preferably spirals around the catheterreceiving lumen 88 as illustrated in FIGS. 12C and 12D. The drugdelivery lumen 92 preferably has a diameter/width of about0.0005″-0.005″ and more preferably about 0.001″-0.003″.

[0130] The drug delivery ports 94 are positioned close enough to achievea substantially even flow of drug solution around the circumference ofthe sheath 82. The proximity of adjacent drug delivery ports 94 can bechanged by changing the density of drug delivery ports 94 along the drugdelivery lumen 92 or by changing the number of windings of the drugdelivery lumen 92 around the energy delivery section 90. Suitabledisplacement between adjacent drug delivery ports 94 includes, but isnot limited to, from 0.1″ to 1.0″, preferable 0.2″ to 0.6″.

[0131] The size of the drug delivery ports 94 can be the same or changealong the length of the drug delivery lumen 92. For instance, the sizeof the drug delivery ports 94 distally positioned on the drug deliverysection can be larger than the size of the drug delivery ports 94 whichare proximally positioned on the drug delivery section. The increase insizes of the drug delivery ports 94 can be designed to produce similarflowrates of drug solution through each drug delivery port 94. Thissimilar flowrate increases the uniformity of drug solution flowratealong the length of the sheath 82. When the drug delivery ports 94 havesimilar sizes along the length of the drug delivery lumen 92, a suitablesize for a drug delivery port includes, but is not limited to 0.0005″ to0.0050″. When the size of the drug delivery ports 94 changes along thelength of the drug delivery lumen 92, suitable sizes for proximallypositioned drug delivery ports 94 includes, but is not limited to from0.0001″ to 0.005″ and suitable sizes for distally positioned drugdelivery ports 94 includes, but is not limited to, 0.0005″ to 0.0020″.The increase in size between adjacent drug delivery ports 94 can besubstantially uniform between or along the drug delivery lumen 92. Thedimensional increase of the drug delivery ports 94 is dependent uponmaterial and diameter of the drug delivery lumen 92. The drug deliveryports 94 can be formed by burnt into the sheath 82 with a laser.

[0132] Uniformity of the drug solution flow along the length of thesheath 82 can also be increased by increasing the density of the drugdelivery ports 94 toward the distal end of the drug delivery lumen 92.

[0133] The drug delivery ports 94 can optionally be closed slits in thesheath 82. The slits can have a straight or arcuate shape. When the dugdelivery lumen 92 contains drug solution, the slits remain closed untilthe pressure within the drug delivery lumen 92 exceeds a thresholdpressure. As the pressure within the drug delivery lumen 92 builds thepressure on each of the slits will be approximately uniform. Once, thethreshold pressure is reached, the uniform pressure will result in theslits opening almost simultaneously and cause a nearly uniform flow ofdrug solution out of all the slits. When the pressure within the drugdelivery lumen 92 falls below the threshold pressure, the slits closeand prevent delivery of additional drug solution. The stiffer thematerial used to construct the drug deliver lumen 38, the higher thethreshold pressure required to open the slit shaped drug delivery ports94. The slit shape can also prevent the drug delivery ports 94 fromopening when exposed to low pressures from outside the sheath 82. As aresult, slit shaped drug delivery ports 94 can maximize control of drugdelivery.

[0134] FIGS. 13A-13G illustrate a method for using the catheter with asheath 82. In FIG. 13A, a guidewire is directed through vessels toward atreatment site which includes a clot. The guidewire is directed throughthe clot. Suitable vessels include, but are not limited to,cardiovascular vessels, the pancreas, sinuses, esophagus, rectum,gastrointestinal vessels and urological vessels.

[0135] In FIG. 13B, the catheter receiving lumen 88 of the sheath 82 isslid over the guidewire and the sheath 82 is advanced along theguidewire using traditional over-the-guidewire techniques. The sheath 82is advanced until the sheath distal end 86 is positioned at the clot.Radio opaque markers may be positioned at the sheath distal end 86 toaid in the positioning of the sheath 82 within the treatment site.

[0136] In FIG. 13C, the guidewire is withdrawn from the utility lumen 38by pulling the guidewire proximally while holding the sheath 82stationary. In FIG. 13D, a drug solution source is coupled with the druginlet port. The drug solution source can be a syringe with a Luerfitting which is complementary with the drug inlet port. Pressure can beapplied to a plunger on the drug solution source to drive the drugsolution through the drug delivery lumen 92. The drug solution isdelivered from the drug delivery lumen 92 through the drug deliveryports 94 as illustrated by the arrows in FIG. 13E. Suitable drugsolutions include, but are not limited to, an aqueous solutioncontaining Heparin, Uronkinase, Streptokinase, or tissue PlasminogenActivator (TPA).

[0137] In FIG. 13F, the catheter is inserted into the catheter receivinglumen 88 until the ultrasound assembly 10 is positioned at the sheathdistal end 86. To aid in placement of the catheter within the sheath 82,radiopaque markers may be positioned on the catheter adjacent to each ofthe ultrasound transducers 20. Alternatively, the ultrasound transducers20 themselves can be radiopaque. Once the catheter is properlypositioned, the ultrasound transducer 20 is activated to deliverultrasound energy through the sheath 82 to the treatment site. Suitableultrasound energy is delivered with a frequency from 5 KHz to 100 MHz,more preferably from 10 KHz to 25 MHz and most preferably from 20 KHz to5 MHz. While the ultrasound energy is being delivered, the ultrasoundtransducer 20 can be moved within the energy delivery section 90 asillustrated by the arrows labeled A. The movement of the ultrasoundtransducer 20 within the energy delivery section 90 can be caused bymanipulating the body proximal section while holding the sheath proximalend 84 stationary.

[0138] While the present invention is disclosed by reference to thepreferred embodiments and examples detailed above, it is to beunderstood that these examples are intended in an illustrative ratherthan limiting sense, as it is contemplated that modifications andcombinations will readily occur to those skilled in the art, whichmodifications and combinations will be within the spirit of theinvention and the scope of the appended claims.

What is claimed is:
 1. An catheter system, comprising: a catheter bodyhaving a chamber containing a low acoustic impedance medium, thecatheter body including an elongated body with an external surface andan ultrasound transducer having an external side between a first end anda second end, the ultrasound transducer positioned over the externalsurface of the elongated body such that the first end is adjacent to thechamber.
 2. The system of claim 1 wherein the ultrasound transducersurrounds the elongated body.
 3. The system of claim 1 wherein thechamber surrounds the elongated body.
 4. The system of claim 1 thecatheter body includes a collar positioned over the elongated body so asto at least partially define the chamber.
 5. The system of claim 4,wherein the catheter body includes a transducer sheath positioned overthe ultrasound transducer and the collar so as to at least partiallydefine the chamber.
 6. The system of claim 4 wherein the catheter bodyat least partially defines a second chamber adjacent to the second endof the ultrasound transducer, the second chamber containing a lowacoustic impedance medium.
 7. The system of claim 6, wherein the secondchamber surrounds the elongated body.
 8. The system of claim 7, whereinthe catheter body includes a collar positioned over the elongated bodyso as to at least partially define the second chamber.
 9. The system ofclaim 8, wherein the catheter body includes a transducer sheathpositioned over the ultrasound transducer and the collar so as to atleast partially define the second chamber.
 10. The system of claim 9,wherein the catheter body includes an assembly sheath positioned overthe transducer sheath.
 11. The system of claim 10 wherein a bindingmedium occupies a volume between the assembly sheath and the transducersheath.
 12. The system of claim 1 wherein the catheter body at leastpartially defines a third chamber between the ultrasound transducer andthe external surface of the elongated body, the third chamber containinga low acoustic impedance medium.
 13. The system of claim 12, wherein thethird chamber surrounds the elongated body.
 14. The catheter of claim12, wherein the catheter body includes a member positioned between theultrasound transducer and the external surface of the elongated bodysuch that the third chamber is positioned between the member and theexternal surface of the elongated body.
 15. The system of claim 13wherein the catheter body includes spacers positioned between the memberand the external surface of the elongated body.
 16. The system of claim12 wherein the catheter body includes an extension body which gives thecatheter length coupled with the elongated body.
 17. The system of claim16 wherein the catheter body includes a sheath over at least a portionof the extension body and over at least a portion of the elongated body.18. The system of claim 3, wherein the chamber and the third chamber areopen to one another.
 19. The system of claim 1, further comprising: asheath having a utility lumen sized to receive the catheter body. 20.The system of claim 19, wherein the utility lumen is sized such that thecatheter body can slide within the utility lumen.
 21. The system ofclaim 1 wherein the sheath includes a drug delivery lumen.
 22. Thesystem of claim 21 wherein the drug delivery lumen spirals around theutility lumen.
 23. The system of claim 21 wherein the drug deliverylumen includes a plurality of ports which permit a drug to flow throughthe ports when a target pressure is achieved within the drug deliverylumen.
 24. The system of claim 21 wherein the drug delivery lumenincludes a plurality of ports which increase in size toward a distal endof the sheath.
 25. The system of claim 1, a lumen sized to receive aguidewire extends longitudinally through the catheter body.
 26. Thesystem of claim 1, wherein the catheter body includes a secondultrasound transducer having a side between a first end and a secondend.
 27. The system of claim 26, wherein the catheter body includes asecond chamber adjacent an end of the second ultrasound transducer. 28.The system of claim 26, wherein the catheter body includes a thirdchamber between the ultrasound transducer and the external surface ofthe elongated body and between the second ultrasound transducer and theexternal surface of the elongated body.
 29. The system of claim 1,wherein the low acoustic impedance medium has an acoustic impedance ofabout 0-1.7 Megarayls.
 30. The system of claim 1, wherein the lowacoustic impedance medium has an acoustic impedance of about 0-0.7Megarayls.
 31. The system of claim 1, wherein a binding medium having anacoustic impedance of about 1.3-10 Megarayls is positioned adjacent tothe external surface of the ultrasound transducer.
 32. The system ofclaim 1, wherein a binding medium having an acoustic impedance of about4-8 Megarayls is positioned adjacent to the external surface of theultrasound transducer.
 33. The system of claim 1, wherein a bindingmedium is positioned adjacent to the external surface of the ultrasoundtransducer and a ratio of acoustic impedances for the binding mediumadjacent to the external side relative to the low acoustic impedancemedium is about 1.5 o 10,000:1.
 34. The system of claim 1, wherein abinding medium is positioned adjacent to the external surface of theultrasound transducer and a ratio of acoustic impedances for the bindingmedium adjacent to the external side relative to the low acousticimpedance medium is about 1.5 to 4:1.
 35. A method for forming acatheter, comprising: positioning an ultrasound transducer over anexternal surface of an elongated body; positioning a collar over theexterior surface of the elongated body such that at least a portion ofthe collar is spaced apart from the ultrasound transducer; andpositioning a transducer sheath over at least a portion of theultrasound transducer and over at least a portion of the collar to forma chamber between the ultrasound transducer and the collar.
 36. Themethod of claim 35, further comprising: positioning a spacer over theelongated body before positioning the ultrasound transducer over theexternal surface of the elongated body.
 37. The method of claim 36,further comprising: positioning a member over at least a portion of thespacer before positioning the ultrasound transducer over the externalsurface of the elongated body.
 38. The method of claim 37, wherein theultrasound transducer is positioned over the member.
 39. The method ofclaim 35, further comprising: positioning spacers over the externalsurface of the elongated body; positioning a member over at least aportion of the spacers such that a chamber is defined between the memberand the external surface of the elongated body; and positioning theultrasound transducer over the member.
 40. The method of claim 35,wherein the collar is integral with a spacer such that the collar has aspacer region and a collar region.
 41. The method of claim 40, furthercomprising: positioning a member over the spacer region of the collarafter positioning the collar over the external surface of the elongatedbody; positioning the ultrasound transducer over the member; andpositioning the transducer sheath over the collar region of the collar.42. The method of claim 35, further comprising: positioning a secondcollar over the external surface of the elongated body such that aportion of the second collar is spaced apart from the ultrasoundtransducer.
 43. The method of claim 42, wherein positioning thetransducer sheath includes positioning the sheath over at least aportion of the second collar to form a second chamber between theultrasound transducer and the second collar.
 44. The method of claim 35,further comprising: positioning an assembly sheath over the transducersheath.
 45. The method of claim 44, further comprising: delivering abinding medium into a volume between the assembly sheath and thetransducer sheath.
 46. The method of claim 35, further comprising:positioning a catheter sheath over the elongated body and at least aportion of an extension body.
 47. The method of claim 46, furthercomprising: delivering a binding medium into a volume between theultrasound transducer and the catheter sheath.
 48. The method of claim46, further comprising: delivering a binding medium into a volumebetween the ultrasound transducer and the extension body.
 49. A methodfor forming a catheter, comprising: positioning a first spacer over anexternal surface of an elongated body; positioning a member over atleast a portion of the first spacer; and positioning an ultrasoundtransducer over the member.
 50. The method of claim 49, furthercomprising: positioning a second spacer over the external surface of theelongated body before positioning the member over at least a portion ofthe first spacer.
 51. The method of claim 50, wherein positioning themember over at least a portion of the first spacer includes positioningthe member over at least a portion of the second spacer to form achamber between the member and the external surface of the elongatedbody.
 52. The method of claim 49, further comprising: positioning asecond spacer such at least a portion of the second spacer is betweenthe member and the external surface of the elongated body.
 53. Themethod of claim 49, further comprising: positioning a collar over theexterior surface of the elongated body such that at least a portion ofthe collar is spaced apart from the ultrasound transducer.
 54. Themethod of claim 53, further comprising: positioning a transducer sheathover at least a portion of the ultrasound transducer and over at least aportion of the collar to form a chamber between the ultrasoundtransducer and the collar.
 55. The method of claim 49, wherein the firstspacer is integral with a collar such that the spacer has a spacerregion and a collar region.
 56. The method of claim 55, whereinpositioning the member over at least a portion of the first spacerincludes positioning the member over at least a portion of the spacerregion of the first spacer.
 57. The method of claim 56, furthercomprising positioning a transducer sheath over at least a portion ofthe ultrasound transducer and over at least a portion of the collarregion of the first spacer to form a chamber between the ultrasoundtransducer and the collar.
 58. The method of claim 57, furthercomprising: positioning a second collar over the external surface of theelongated body such that a portion of the second collar is spaced apartfrom the ultrasound transducer.
 59. The method of claim 57, whereinpositioning the transducer sheath includes positioning the sheath overat least a portion of the second collar to form a second chamber betweenthe ultrasound transducer and the second collar.
 60. The method of claim59, further comprising: positioning an assembly sheath over thetransducer sheath.
 61. The method of claim 60, further comprising:delivering a binding medium into a volume between the assembly sheathand the transducer sheath.
 62. The method of claim 49, furthercomprising: positioning a catheter sheath over the elongated body and atleast a portion of an extension body.
 63. The method of claim 62,further comprising: delivering a binding medium into a volume betweenthe ultrasound transducer and the catheter sheath.